<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        let a = 1
        let b = 2
        let c = "xx"
        let d = "yy"
        switch (a){
            case 1:
                alert("a等于1")
                break;
            case 2:
                alert("a等于1")
                break;
            case 3:
                alert("a等于1")
                break;
            default:
                alert("a不等于123")
                break;
        }
    </script>
</head>
<body>

</body>
</html>